tioii iCiirt aiui Stiill. ]'X\\ ; W iritiold. l<):f.'ili ; Wiiiticld and e'liiii, 

 l!i;iS). Also, ill North C'liina, Wiiiliold and Yao (I'.CiT) eould 

 tiiid no evidence of asearis eggs on vegetables after they were 

 prei>ared for food, and expressed the opinion that infection 

 from this source was of little if any significance in this part 

 of China. It seems clear, however, that the use of human ex 

 crenieiit as fertilizer does spread asearis probably in a number 

 of different ways, since in China, Korea, and Japan infection 

 witli this parasite appears to be more common, especially in the 

 atlults, than anywhere else in the world. 



CONTROL OF ASCAEIASIS 



Treatment of infected populations and improvement in house- 

 hold sanitation are the obvious suggestions for the control of 

 ascariasis. On account of the enormous numbers of eggs pro- 

 duced and their great resistance to chemicals, sterilization of 

 sources of infection \vould seem to have a very limited value. 



In spite of the availability of effective nntlieliuintics (Brown, 

 ]!'34), there is clear evidence that mass treatment of infected 

 pojuilations is not an effective control measure against asearis 

 because of rapid reinfection (Cort, Schapiro, and Stoll, 1929; 

 Otto, 1930; Otto and Cort, 1934b). Perhaps if the treatments 

 could be made almost 100 percent effective in removing the 

 worms, and if they were administered at the end of a dr}' 

 season or winter when the numbers of viable eggs in the soil 

 would be reduced (Cort, Schapiro, Riley, and Stoll, 1929), they 

 might have some real value as a control measure. At any rate, 

 treatment in ascarisinfected populations is imi)ortant for re- 

 lieving heavily infected individuals, especially young children, 

 of dangerous worm burdens. 



There are also certain difficulties to be met in the attempt to 

 control asearis by improved sanitation (Cort, 1931, p. 137). 

 It was found in Panama (Cort, Stoll, Sweet, Riley, and Scha- 

 piro, 1929) that in certain areas sanitary improvements that 

 had definitely reduced the level of hookworm infection did not 

 appear to limit the spread of asearis. Also, more than half of 

 the families with heavy asearis infection that were studied in 

 the mountains of Tennessee had privies which in almost all 

 cases were in use (Otto, Cort, and Keller, 1931). Examples have 

 also been reported from cities of families with flush toilets 

 connected with the sewage system in which the children had 

 considerable asearis infection (Otto and Cort, 1934a; Headlee, 

 193(5). Under all these conditions the infection is kept up be- 

 cause the young children fail to use the sanitary facilities and 

 deposit their stools in the yards close to the houses. 



In attempts to improve sanitation in rural districts certain 

 practical points of special importance in the control of asearis 

 seem to have been entirely overlooked in a number of places. 

 First, the latrines should lie placed near enough to the houses 

 so that they can be reached by the young children, and in the 

 second place they should have special seats for the children. 

 Usually seats are designed only for adults and are difficult or 

 even dangerous for children to use. In addition, real progress 

 in asearis control will have to depend on the instruction of the 

 children and their parents in the homes and in the schools in 

 the dangers of soil pollution and in the minimum requirements 

 of a proper household sanitation. In most places widespread 

 asearis infection is associated with general low standards of 

 living, and any raising of standards will have a tendency to 

 reduce infection. 



Trichuris trichiura 

 W. W. C. 



The whipworm, Tricliiiri.i tricliiiira, was first described by 

 Roederer in 1761, although it was apparently observed much 

 earlier. Davaine (18.")S and 18(53) studied the development of 

 the eggs. Leuckart (1866) demonstrated experimentally the 

 direct development of the trichuris of the sheep and pig, and 

 Grassi (1887) produced experimental infection with T. tricliiiira 

 in man. About the liegiuning of the 20th century the patho 

 genie role of trichuris was greatly emphasized and it was con- 

 sidered to be an important factor in infection with such dis- 

 eases as typhoid fever, cholera, appendicitis, and dysentery 

 (Guiart, 1911). More recently, however, these views have been 

 discounted by most workers. The extensive surveys of the last 

 three decades by fecal examination have greatly extended the 

 knowledge of the distribution of trichuris. Also, considerable 

 information on the factors influencing its dissemination has 

 been obtained, chiefly in connection with field studies on as- 

 earis and hookworm. 



The adults of T. trichiura are most frequently found in the 

 caecum, vermiform appendix, and colon with their long at- 

 tenuated anterior ends sewed into the superficial mucosa. The 

 great majority of infections with the human trichuris involve 

 only a few worms, but in occasional cases hundreds may be 

 present. The length of life of the adult worms is not definitely 

 known, although it appears to be much greater than that of 



ascaiis. .Mso, there is no evidence of the constant loss of worms 

 and rapid turnover of infections found in that species. There 

 is some evidence that an acquired immunity is developed in 

 trichuris infections (Suzuki, 1934; Miller, 1941). 



PATIIOGKNECITV 

 The adult worms produce some injury to the int<'stinal mu- 

 cosa and when present in large numbers may cause considerable 

 inflammation. Therefore, in the heaviest cases they may pro 

 duee rather severe intestinal disturbances. There is no real 

 evidence that they serve as a "lancet of infection" for other 

 diseases as suggested by many earlier workers (Guiart, 1911) 

 and their relation to the production of anemia is rather doubt- 

 ful (Otto, 1935; Swartzwelder, 1939). In most cases their 

 presence would pass unnoticed except for the finding of the 

 characteristic eggs in fecal examinations. 



DISTRIBUTION AND EPIDEMIOLOGY 



Trichuris trichiura is widely distributed in the world and 

 is frequently found, especially in tropical and subtropical re- 

 gions, associated with both asearis and hookworm. Its range 

 is not as extensive as that of asearis, especially in the temperate 

 zones and it is absent in the colder regions. In the majority 

 of places where both these parasites are found together the in- 

 cidence of trichuris is lower. In the mountain regions of the 

 southeastern United States, where the incidence of asearis is 

 several times that of trichuris, families are common that harbor 

 only asearis, but almost always where trichuris is f(Hind as- 

 earis will also be present (Otto, Cort, and Keller, 1931). There 

 are, however, many situations where examinations have shown 

 the incidence of trichuris to be equal to or even higher than that 

 of asearis. Such situations are usually in tropical or subtropical 

 countries, but there are a number of places in Europe, especial- 

 ly in the U. S. S. R., where the incidence of trichuris is sur- 

 prisingly high. 



Examinations of the last few years by the dilution egg-count- 

 ing method have given us considerable information on the dis- 

 tribution of trichuris within population groups, especially in the 

 United States (Cort, Stoll, Sweet, Riley, and Schapiro, 1929; 

 Otto, Cort, and Keller, 1931; Cort and Otto, 1937). Its dis- 

 tribution resembles that of asearis in having the family as the 

 unit of dissemination, and in the concentration of a large pro- 

 portion of the worm burden in a small percentage of heavy 

 cases, usually grouped in families. Also, the distribution of 

 trichuris according to age and sex is much like that of asearis 

 except that the peak of infection comes almost always at a 

 somewhat later age. Usually adult females are more heavily 

 infected than males of the same age groups. 



The human habits involved in the spread of trichuris and 

 asearis appear to be exactly the same. Differences in egg 

 production, susceptibility of hosts to infection, stability and 

 persistence of infection in the hosts, or in immunity relations 

 cannot be evaluated in the present state of our knowledge in 

 relation to differences in the methods of dissemination or dis- 

 tribution of these two parasites. Therefore, in attempting to 

 explain such differences we must concern ourselves chiefly with 

 the differences that have Iteen found in the resistance of 

 their eggs to external environmental factors. The eggs of tri- 

 churis are much less resistant to low temperatures than are 

 those of asearis, and are somewhat less resistant to high tem- 

 peratures (Nolf, 1932). They are also less resistant to desic- 

 cation, require slightly more moisture for development, and de- 

 velop more slowly when the moisture is reduced (Caldwell and 

 Caldwell, 1928; Spindler, 1929 a & b; Nolf, 1932; Onorato, 

 1932). They are very long lived and like those of asearis are 

 very resistant to chemicals, and they are considerably more 

 resistant than the eggs of asearis to ultra violet light (Nolf, 

 1932). 



The differences just discussed in the resistance to external 

 environmental conditions of the eggs of asearis and trichuris 

 appear to exjjlain .satisfactorily at least some of the differences 

 in their distribution. Certainly the absence of trichuris in cold 

 regions and its scarcity wherever there is a long cold winter 

 can be explained on the basis of the lack of resistance of its 

 eggs to low temperatures. It seems unlikely that the eggs of 

 trichuris on the soil could live through even a short period of 

 freezing temperatures. 



Following suggestions that trichuris is limited more in its 

 distribution by dry conditions than asearis (Sweet, 1924; 

 Chandler, 1928), this relation was first carefully studied by 

 Spindler (1929b) in the United States. It was found that in 

 the mountains of southwestern Virginia trichuris occurred in 

 a much lower incidence than asearis except in a few limited 

 localities, where dense shade in the yards produced moist con- 

 ditions where the eggs were deposited. This finding led to the 

 suggestion supported by a careful review of the literature that 

 the incidence of trichuris tends to be as great or greater than 

 asearis onlv where there is a considerable amount of moisture 



Sl.j 



